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Mowing Makes It Worse – for Oct. 8, 2009

Mowing ditches may be doing more than just making the roads look pretty, reducing the odds of wildlife jumping out in front of cars, and preventing snow buildup in winter.

It may be speeding up the spread of leafy spurge and other troublesome weeds.

A study published in Invasive Plant Science and Management, the journal of the Weed Science Society of America, found a greater distribution of invasive plants in proximity to forest roads, which provide corr idors that facilitate the dispersal of plant material.

Wayne Digby, chair of the Leafy Spurge Stakeholders Group, said that it has long been known on the leafy spurge-plagued Prairies that there is a strong link between road maintenance and the spread of invasive weed species.

The problem is getting everyone to recognize that spurge is a major problem, and that they need to work together to fight it.

“The ideal situation would be one where we could work with municipalities in line with their weed management plans,” he said.

“If we had a good idea where the spurge was, then we could work with their people in managing that spurge and not spreading it,” he said.


The study was conducted in the Green Ridge State Forest in western Maryland along the Potomac River in the United States.

The forest has a mix of protected natural areas managed by The Nature Conservancy and spaces for recreational use. The 32,000-ha area is dissected by paved and unpaved roads and trails.

Researchers recorded the presence and per cent cover of more than a dozen species of invasive plants, the most prominent being Japanese stiltgrass, Microstegium vimineum.

Patches of Japanese stiltgrass were deliberately planted and allowed to expand naturally over the course of four years before being controlled. This natural spread was found to be much slower than the spread of the plant adjacent to roadways, as observed by forest managers.

John Johnston, a weed supervisor for the Southwest Weed District, which includes four rural municipalities, said that weed fighters have a good working relationship with highway maintenance officials, but better communication and more flexible mowing schedules would help.


Currently, he noted, the work is subcontracted mainly to local farmers. They are required to mow at least as close to July 1 as possible, then once more before or around Sept 1.

“Depending on the year, heat units and growth, (spurge) can be producing seed pods as early as the second week of June,” said Johnston.

If that’s the case, the rotary mowers used to clear the 15-foot swath required by the highways authorities could be scattering seed in every direction. And if the mowers aren’t carefully cleaned afterwards, then the problem could be spread anywhere that machine might go, he added.

Right now, it’s obvious that spurge is moving up Hwy. 10 towards Riding Mountain National Park.

“It’s quite often about 15 to 30 feet off the shoulder, so that’s about the far edge of the mowers,” said Johnston.

Mowing doesn’t do much more than stop the plants from setting seed, however. The massive root system continues to spread up by up to three feet a year underground, even if it is constantly mowed.

That means controlling

“Once it’s

established, you have it forever.”


the spread of seed is critical, he said.

“One thing we’ve emphasized to them is to ask their contractors to sweep off their mowers as they move along the highway, maybe every couple of miles, or at municipal boundaries,” said Johnston.

“I’m not sure it’s happening, but we’ve requested that.”


Keith Loney, a weed supervisor based near Carberry, added that spurge-infested gravel pits are a serious problem, too. Weed seed gets mixed in with the gravel and then is transported far and wide.

“If it gets in there, then you’re bound to get it hauled to your municipality,” he said.

One thing is cer tain about leafy spurge, said Johnston, is that vigilance and prevention offer the only way to keep the hardy and aggressive plant at bay. His annual budget for all weed and brush control is $175,000, plus another $20,000 or so for chemical to cover four R. M. s.

Spending $1,000 to kill a single leafy spurge plant – if it was the only one in a new, pristine area – would be a bargain, said Johnston.

“Once it’s established, you have it forever,” he said. “If you can get it in that first year, before it sets seed and establishes a root system, it’s uncountable how much money that would save.” [email protected]

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